1. Field of the Invention
This invention relates to an information signal recording apparatus and, more particularly, to an apparatus for recording main information signals in tracks formed on a recording medium. Still more particularly, it relates to an apparatus for recording not only main information signals, but also additional information signals.
2. Description of the Related Art
The following in this written specification is described by taking an example of a helical scan type video tape recorder (VTR) as the apparatus of this kind.
The helical scan type VTR has been known to provide a model in which a magnetic tape is wound around a cylinder in an angular coverage of 221.degree., the cylinder having a pair of recording or reproducing rotary magnetic heads located in spaced relation by an angular difference of 180.degree.. Of the coverage, a region of 180.degree. is assigned to recording of video signals, and another region of 36.degree. to recording of sound signals compressed in the time axis.
FIG. 1 shows an example of the record format of such a model of VTR. The rotary magnetic head starts to contact the tape from the left side and forms a helical track. Within this helical track, there is provided an inrush portion 6 of 5.degree. in rotation angle, of which the latter part of 2.06.degree. forms a clock run-in portion 7 to make synchronize it with PCM data. This clock run-in portion 7 is followed by a time-axis-compressed PCM audio data portion 8 of 26.32.degree.. Successive to this PCM audio data portion 8 there is provided a back margin portion 9 of 2.06.degree. to cope with the recording position gap produced when after-recording by the difference between apparatus. Between the PCM audio data portion 8 and the next video signal portion 11 there is further a guard band portion 10. The next 180.degree. part contains a video signal portion 11 and a separation portion 12 of 5.degree..
According to such a record format, the video signals for every one field are recorded in, or reproduced from, the video signal portion 11 of every one track, while the PCM audio data obtained by compressing the audio signal for 1/60 sec. in the time axis is recorded in, or reproduced from, the PCM data portion 8.
Meanwhile, the video signal portion 11 in the record format described above is divided into five parts, so that, as they are equalized to each other, each subtends 36.degree., thus totaling six segments in constituting the PCM audio portion. Such a record format, too, has been proposed. FIG. 2 shows this record format adapted solely to be used for PCM audio data. First of all, each track has six segments 5, 13, 14, 15, 16 and 17, of which the first segment 5 comprises the aforesaid inrush portion 6 of the rotary head through the guard band portion 10, the next or second segment 13 is constructed in the same form, comprising an inrush portion 19, a clock run-in portion 20, a PCM data portion 21, a back margin portion 22 and a guard band portion 23, and the third to the sixth segments 14, 15, 16 and 17 are formed likewise.
The use of such a record format provides a possibility of recording or reproducing PCM audio data independent of each other in the respective segments. Also, by using the flying erase head, it is also possible to erase the PCM audio signal of the desired segment and then rewrite in this segment.
With the conventional VTR model having the fixed head, heading signal time code, date and other items of additional information, are generally recorded by that fixed head in the track assigned to the control (CTL) signal for tracking along with the CTL signal.
Without using the fixed head, the aforesaid additional information may be recorded only by the rotary head. In a known method, besides the area assigned to record the main information signals, such as video signals and audio signals, there is provided a recording area for the additional information, and the items of additional information to be recorded in this new area are broadened.
Also, as to the recording signal form of this additional information, either digital signals or analog signals has been proposed.
Meanwhile, in recent years, use of a new type of VTR with a video camera in unified form, or a so-called camera-unified type VTR, is spreading.
FIG. 3 shows an example of the construction of the conventional camera-unified type VTR. A time information recording and reproduction device in the camera-unified type VTR comprises, as shown in FIG. 3, a time code generator 36 and a character generator 35 responsive to the time code for producing an output signal which is then multiplexed by an adder 34 on the video signal produced from the known circuit comprising an image sensor 32 with an optical system 31, a camera signal processing circuit 33 and others. In short, it has been the common practice that the time code is recorded as the character information in the form of a video signal. This character information-multiplexed video signal, along with four pilot signals (4f) to be used in the 4-frequency type tracking control of audio signals, is converted to a recording signal of the form suited to be recorded by a recorder signal processing circuit 37. This recording signal passes through an amplifier 38 and a head switch 41 to the rotary heads 39-a and 39-b by which it is recorded on a tape-shaped recording medium or magnetic tape 40.
When the aforesaid signal is reproduced, the recorded information of the time code generator 36 appears in a portion of the picture taken by the optical system 31.
Another method of recording the time code is by using the longitudinal track formed in the vicinity of the tape. Yet another method is to create a sub-code recording area in each track as separated from the recording area for the main information so that the time code is recorded as a sub-code in this sub-code recording area.
By the way, in a case where the time code is recorded as the character information in the form of a video signal, because it is multiplexed on the video signal, it always is displaced in superimposed relation on the picture when reproduced. Therefore, when reproducing, the date letters and the picture cannot be separated from each other. Also, in recording foreseeing whether the date will be necessary or unnecessary when reproducing, the photographer must determine in advance which position the selector switch should be set in. Further, this leads to the impossibility of knowing the time information of those picture frames which lack the character information representing the time code imposed thereon.
Also, in a case where the time code is recorded in the longitudinal track, because the relative speed of the tape and the fixed head is low, a lot of information cannot be expected to record. Therefore, it is difficult to record those fractions of the time code which are in shorter time units, and a wide variety of items of additional information. Further, because the necessity of providing the fixed head arises, it is unfavorable since the tape will wear out fast and an increase of the complexity of the mechanisms is called for.
Further, in a case where the time code is recorded as a sub-code in the sub-code recording area provided in each track, this sub-code information is difficult to read when in reproduction with the tape running at a high speed, for example, for forward or backward searching of the VTR. This tendency is more prominent particularly when the so-called azimuth recording is effected.
In more detail, generally when the additional information is recorded as the digital signal, the additional information is hardly extracted at the time of the fast running of the tape. This arises because the clock synchronism is broken due to the change of the relative speed of the head and the tape from when usually recorded. Also, when the so-called azimuth recorded tape is reproduced, the rotary heads are caused to move across some tracks. Therefore, the difficulty of extracting the additional information is increased.
Meanwhile, in a case where the additional information is recorded as the analog signal, regardless of the speed of transportation of the tape, the additional information can be extracted relatively easily. However, generally the track cannot afford so much large recording area as the additional information recording area. In accompaniment with this, the quantity of additional information available to record in the form of analog signals is caused to be very little.